Calcium chloride
5 marks · HardCalcium chloride is formed when calcium reacts with chlorine.
State the electronic configuration of a calcium atom and a chlorine atom.
Explain how calcium and chlorine atoms achieve full outer shells when forming calcium chloride.
Draw a dot-and-cross diagram to show the ions formed in calcium chloride. Show only the outer shells.
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(a) Calcium atom: [2,8,8,2]; Chlorine atom: [2,8,7]
(b) The calcium atom loses two electrons, one to each chlorine atom. Each chlorine atom gains one electron. This allows all the atoms to achieve full outer electron shells, forming Ca2+ and Cl- ions.
(c) Diagram shows Ca2+ with no electrons in outer shell, each Cl- ion with 8 electrons (7 original + 1 gained, different symbols for original and gained electrons). Charges shown. · must show Ca2+ ion with empty outer shell, Each Cl- ion with 8 outer electrons, with one electron as dot/cross from Ca, Key or clear use of dots and crosses, Charges shown
Common mistakes: Incorrect electron counts; Electrons shared, not transferred; Wrong dot-and-cross representation
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Marking points
B1 (a) · 1 mark · States correct electronic configurations for calcium and chlorine atoms.
M1 (b) · 1 mark · Explains calcium atom loses two electrons and each chlorine atom gains one.
M2 (b) · 1 mark · Links this transfer to achieving full outer shells for all atoms.
D1 (c) · 1 mark · Correctly shows Ca2+ and Cl- ion arrangement with dot-and-cross notation for electrons (only outer shells).
D2 (c) · 1 mark · Shows appropriate charges on ions and correct number of electrons in each ion's outer shell.
Worked solution
(a) Calcium atom: [2,8,8,2]; Chlorine atom: [2,8,7].
(b) Each calcium atom has two electrons in its outer shell and loses both, one to each chlorine atom. Each chlorine atom gains one electron to fill its outer shell. As a result, calcium forms a Ca2+ ion and chlorine forms Cl- ions, all with full outer shells.